1. Field of the Invention
The present investigation generally relates to shoe sole and heel structures having fluid-containing cavities for providing a cushioning effect for a wearer's feet, and for assisting the wearer during walking or running by providing thrust which facilitates such motion.
2. Description of the Related Art
It is known, for example, from U.S. Pat. No. 4,237,625, U.S. Pat. No. 4,577,417 and U.S. Pat. No. 5,524,364 to provide a shoe structure having a resilient outsole with metatarsal and heel bulges bounding air-filled cavities, and a restricted passageway formed in the outsole and extending between the cavities. Air moves back and forth between the cavities along the restricted passageway. The known shoe structures provide a measure of cushioning for the wearer's feet, and also provide a forward thrust to help propel the wearer during walking and running. Other shoe constructions, such as exemplified by U.S. Pat. No. 4,016,662, U.S. Pat. No. 5,701,687, U.S. Pat. No. 5,706,589 and U.S. Pat. No. 5,771,606, disclose the use of air bladders within the shoes to provide such cushioning and thrust.
As advantageous as these known shoe structures have been, experience has shown that the restricted passageway becomes at least partially obstructed during walking and running movement, thereby compromising the free flow of air between the cavities. As the resilient outsole is flexed, twisted and otherwise deformed during movement, the passageway, which is molded into the outsole, likewise participates in this deformation, with the result that there are times when creases in the outsole extend across the passageway and impede air flow therealong. This degrades the generation of forward thrust.